linux-kernel - Re: [PATCH] i2c: tegra: Wait for config load atomically while in ISR

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Message-ID: <9ba3d704-674b-94df-d10f-e3edb3c695d6@kapsi.fi>
Date:   Mon, 11 Jan 2021 16:38:06 +0200
From:   Mikko Perttunen <cyndis@...si.fi>
To:     David Laight <David.Laight@...LAB.COM>,
        'Mikko Perttunen' <mperttunen@...dia.com>,
        "ldewangan@...dia.com" <ldewangan@...dia.com>,
        "digetx@...il.com" <digetx@...il.com>,
        "thierry.reding@...il.com" <thierry.reding@...il.com>,
        "jonathanh@...dia.com" <jonathanh@...dia.com>,
        "wsa@...nel.org" <wsa@...nel.org>
Cc:     "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH] i2c: tegra: Wait for config load atomically while in ISR

Agreed that this is possibly not optimal, but this patch simply returns 
the behavior to what it was before "i2c: tegra: Support atomic 
transfers", fixing the overt issue.

Design fixes can be considered later, in a non-stable patch.

Mikko

On 1/11/21 4:31 PM, David Laight wrote:
> From: Mikko Perttunen
>> Sent: 11 January 2021 13:56
>>
>> Upon a communication error, the interrupt handler can call
>> tegra_i2c_disable_packet_mode. This causes a sleeping poll to happen
>> unless the current transaction was marked atomic. Since
>> tegra_i2c_disable_packet_mode is only called from the interrupt path,
>> make it use atomic waiting always.
> 
> Spin-waiting in an ISR for anything that it makes sense to do
> a sleep-wait for at other times is badly broken design.
> 
> 	David
> 
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